Let's forget Google's interview question. I think this one has more fun to work with: On some island live 100 people, some have blue eyes and some has brown eyes. They have an absolute taboo that they cannot convey any information on eye color, and there is no way they can see their own eye color. It is furthermore an absolute rule that any person who can prove that his/her eyes are blue must, at midnight of the day on such proof, leave the island. Finally, they must gather every day at noon to see if there is anyone left the island. One day, an oracle came to the island and stated: "There is at least one blue-eyed person on this island." What, if anything, happens?
